This invention relates to a method and apparatus for controlling the operation of a multistage hydraulic machine, and more particularly to a method and apparatus for controlling and adjusting a load, in a normal operating condition, of a multistage hydraulic machine in which all pressure stages are interconnected through return passages and the highest and lowest pressure stages are provided with movable guide vanes.
In a known hydraulic machine, the operation or running condition thereof is controlled by adjusting water flow-rate passing through a runner, with adjustment being made on the guide vanes provided around the runner or on an inlet valve provided at an inlet portion of the hydraulic machine. Such a method as described above may be applied to a multistage hydraulic machine in which respective pressure stages are provided with runners and connected together through return passages. However, the control of water flowing conditions at the respective stages by guide vanes provided around the runners of the stages is extremely difficult because of constructional limitations in providing movable guide vanes around the runners of the corresponding stages and in controlling the opening and closing of the guide vanes by a guide vane control mechanism connected to the guide vanes, thus entailing a problem in practical use of the multistage hydraulic machine.
In another controlling method, only stationary guide vanes having a constant degree of opening are provided around the runner of each pressure stage, and the adjustment of the water flow rate and the machine operation control are performed by open-close control of the inlet valve provided at an inlet portion of the hydraulic machine. With this method, however, the water flow condition at the periphery of the runner of each stage cannot be properly adjusted, so that in low and high flow-rate ranges apart from design points, hydraulic performance of the hydraulic machine tends to be deteriorated.
In order to obviate the defects or problems described above, there has been proposed a method for controlling the operation of a multistage hydraulic machine, in which movable guide vanes are provided only for the highest pressure stage and the flow amount of water can be adjusted by regulating the degress of opening of the movable guide vanes. Also, with this method, problems such as vibrations, noises and cavitation tend to occur in case of low flow-rate operation of the hydraulic machine.
It has been considered to construct a multistage hydraulic machine provided with movable guide vanes for the highest and lowest pressure stages for improving the load controlling operation of the machine under a normal operation condition. In this case, the construction of the part forming flow passage is complicated in comparison with that of a hydraulic machine of a single pressure stage, and furthermore the openings of the two sets of movable guide vanes in the highest and lowest pressure stages must be controlled accurately. In case where the movable guide vanes are not controlled accurately, head-share, that is, the ratio of the water pressure or head supported by a specific pressure stage to the water pressure or head supported by the entire stages of the machine, becomes unequal by the pressure stages, thus lowering the hydraulic performance and creating excessive pressure rise or vibrations, noises and cavitation particularly in the lowest pressure stage.
In other words, the technique for controlling multistage hydraulic machines which are provided with movable guide vanes in the highest pressure stage and lowest pressure stage, has not yet been well established, and any appropriate operation control method in which the load of the multistage hydraulic machine is accurately controlled under a normal operating condition, has not yet been proposed.